The Ferguson Hitch: A Virtual Pivot Ahead of the Axle

A plough pinned to a tractor's drawbar behind the rear axle does two bad things: on a hillside it slides downhill with the tractor's tail, and when the driver steers away from a crop row it swings the wrong way first, into the crop. Harry Ferguson of Belfast replaced the pin with two links whose rear ends are wider apart than their front ends. Produced forward, their centre lines meet at a point ahead of the real joints, and the implement swings as if hitched there — so it follows the steering. US 1,916,945, filed 6 June 1929 and granted 4 July 1933, adds a lower link so the implement keeps vertical freedom and an effective line of draft that holds it in the ground, as in his earlier US 1,464,130. This rung finds the virtual centre from the link geometry, shows why it follows the steering, works out how the line of draft loads the rear wheels, and builds a plan-view model to prove it.